Force sensor

Abstract

To obtain a force sensor capable of simplifying a structure and detecting torque with force in each direction of mutually vertical three axes and each of the three axes as a center.SOLUTION: A force sensor 10 includes: a strain element 20 that has a fixing part, a force reception part for receiving a load, a thin-plate part provided in the fixing part, and a bridge girder part for connecting the force reception part to the thin-plate part, where the force reception part travels or turns relative to the fixing part by strain of at least one of the thin-plate part and the bridge girder part when the force reception part receives the load; a magnet mounting plate 40 that is joined to the force reception part; multiple magnets 60 that are mounted to the magnet mounting plate 40; a board 50 that is fixed to the fixing part; and multiple magnetic sensors 70 that are disposed on the board 50 and face the magnet 60 a one-to-one basis, and detect magnetic flux density in each direction of mutually vertical three axes.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to a force sensor that detects a load.

Background Art

[0002] For devices such as the arm of an industrial robot or a medical manipulator, a force sensor that detects the load acting on each part of the device and outputs an electrical signal is used. As force sensors, a strain gauge type force sensor disclosed in Patent Document 1 and a magnetic type force sensor disclosed in Patent Document 2 are known. The force sensor disclosed in Patent Document 1 detects the electrical resistance value of a strain gauge, and detects the force for moving the force receiving body of the force sensor and the torque for rotating the force receiving body based on the amount of change in the magnetoresistance value. The force sensor disclosed in Patent Document 2 includes a magnet and a Hall element which is a magnetic sensor, and detects the force for moving the force receiving body and the torque for rotating the force receiving body by detecting the change in the relative position of the magnet with respect to the magnetic sensor based on the change in the magnetic flux density.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the case of the conventional force sensor disclosed in Patent Document 1, since it is necessary to attach a large number of strain gauges to the strained body in the manufacturing process of the force sensor, the structure of the force sensor becomes complicated. The conventional force sensor disclosed in Patent Document 2 has each of four Hall elements detecting the distance from a magnet, and detecting the forces in two mutually perpendicular biaxial directions and the torque centered on one axis perpendicular to each of the two axes. That is, the force sensor disclosed in Patent Document 2 uses four Hall elements to detect the forces in three mutually perpendicular directions and the torque centered on one axis. Therefore, in order to detect a total of six components of force, namely the forces in three mutually perpendicular directions and the torques centered on each of the three axes, it is necessary to increase the number of Hall elements, so that the structure of the force sensor becomes complicated. Thus, there has been a problem that it is difficult for a conventional force sensor to have a simple configuration and to detect the forces in three mutually perpendicular directions and the torques centered on each of the three axes.

[0005] The present disclosure has been made in view of the above, and an object thereof is to obtain a force sensor that can have a simple structure and can detect the forces in three mutually perpendicular directions and the torques centered on each of the three axes.

Means for Solving the Problems

[0006] In order to solve the above-described problems and achieve the object, the force sensor according to the present disclosure includes a fixed portion, a force receiving portion that receives a load, a thin plate portion provided on the fixed portion, and a bridge portion that connects the force receiving portion to the thin plate portion. When the force receiving portion receives a load, at least one of the thin plate portion and the bridge portion is distorted, so that the force receiving portion moves or rotates with respect to the fixed portion, a strained body, a magnet mounting plate fastened to the force receiving portion, a plurality of magnets attached to the magnet mounting plate, a substrate fixed to the fixed portion, and a plurality of magnetic sensors each arranged on the substrate, facing the magnet one-to-one, and detecting the magnetic flux density in each direction of three mutually perpendicular axes.

Effects of the Invention

[0007] The force sensor according to the present disclosure can have a simple structure and has the effect of being able to detect forces in three mutually perpendicular directions and torques about each of the three axes.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Mode for Carrying Out the Invention

[0009] Hereinafter, the force sensor according to the embodiment will be described in detail with reference to the drawings.

[0010] Embodiment 1. FIG. 1 is a perspective view showing the appearance of the force sensor 10 according to Embodiment 1. FIG. 2 is an exploded perspective view of the force sensor 10 according to Embodiment 1. FIG. 3 is a top view of the force sensor 10 according to Embodiment 1. FIG. 4 is a bottom view of the force sensor 10 according to Embodiment 1. FIG. 5 is a cross-sectional view of the force sensor 10 according to Embodiment 1.

[0011] The X-axis, Y-axis, and Z-axis are three mutually perpendicular axes. Among the directions of each axis, the direction of the arrow is defined as the positive direction, and the direction opposite to the arrow is defined as the negative direction. In Embodiment 1, the positive Z-direction is the upward direction, and the negative Z-direction is the downward direction. The external appearance of the force sensor 10 shown in FIG. 1 is cylindrical. The Z-axis is the height direction of the cylinder, that is, the axis in the height direction of the force sensor 10. Note that the shape of the force sensor 10 is not limited to a cylindrical shape and can be appropriately deformed. FIG. 3 shows the force sensor 10 viewed from the positive Z-direction side. FIG. 4 shows the force sensor 10 viewed from the negative Z-direction side. The cross-section shown in FIG. 5 is the cross-section taken along the V-V line shown in FIG. 3 and is a cross-section parallel to the X-axis and the Z-axis.

[0012] The force sensor 10 includes a strain body 20, a force receiving body 30 provided on the positive Z-direction side of the strain body 20, a magnet mounting plate 40 attached to the strain body 20, a substrate 50 provided on the negative Z-direction side of the strain body 20 and the magnet mounting plate 40, a plurality of magnets 60, and a plurality of magnetic sensors 70. The force receiving body 30, the strain body 20, and the substrate 50 are overlapped with each other in the Z-direction. The magnet mounting plate 40 is sandwiched between the strain body 20 and the substrate 50.

[0013] When the strain body 20 is distorted by a load such as a force or torque to be measured, the position of at least one of the plurality of magnets 60 changes through the magnet mounting plate 40. Due to the change in the relative position between the magnetic sensor 70 and the magnet 60, the magnetic flux density detected by the magnetic sensor 70 changes. The force sensor 10 estimates the applied load based on the amount of change in the magnetic flux density detected by the magnetic sensor 70.

[0014] The force-receiving body 30 is a structure that receives an external force applied from outside the force sensor 10, that is, a load. In the XY plane, the outer shape of the force-receiving body 30 is circular. As the material of the force-receiving body 30, a metallic material such as an aluminum alloy or a steel material is used. The screw holes 31 are formed near the center of the force-receiving body 30 in the X and Y directions. The screw holes 32 are formed near the outer edge of the force-receiving body 30 in the X and Y directions. Four screw holes 31 and four screw holes 32 are formed in the force-receiving body 30 shown in FIG. 3. The number of the screw holes 31 and the number of the screw holes 32 are arbitrary.

[0015] FIG. 6 is a perspective view of the strain-generating body 20 which is a component of the force sensor 10 according to Embodiment 1. In the XY plane, the outer shape of the strain-generating body 20 is circular. As the material of the strain-generating body 20, a metallic material such as an aluminum alloy or a steel material is used. The strain-generating body 20 includes a force-receiving portion 21, four bridge portions 22, four thin plate portions 23, and a fixing portion 25.

[0016] The force-receiving portion 21 is provided at the center of the strain-generating body 20 in the X and Y directions. The force-receiving portion 21 is fastened to the force-receiving body 30 by a fixture such as a screw screwed into the screw hole 31 of the force-receiving body 30 shown in FIG. 3. The surface of the force-receiving portion 21 on the plus Z direction side is in contact with the force-receiving body 30. The force-receiving portion 21 receives the load applied to the force-receiving body 30. Note that a screw or the like, which is a fixture for fixing the detection target and the force-receiving body 30, such as a robot hand such as an electric hand or an air hand, is screwed into the screw hole 32 of the force-receiving body 30. The illustration of the fixture for fastening the force-receiving portion 21 to the force-receiving body 30 and the fixture for fixing the force-receiving body 30 to the detection target is omitted.

[0017] The fixing portion 25 surrounds the outer edge of the strain-generating body 20 in the X and Y directions. Four screw holes 24 are formed in the fixing portion 25. A fixture such as a screw for fixing the fixing portion 25 to a device such as a robot arm is screwed into the screw hole 24. The illustration of the fixture for fixing the fixing portion 25 to the device is omitted.

[0018] The thin plate portion 23 is a flexible thin plate. The thin plate portion 23 is provided on the center side rather than the outer edge of the fixing portion 25. The thickness direction of the thin plate portion 23 is the radial direction of the circle which is the outer shape of the strain generating body 20. The thin plate portion 23 has a shape that is long in the direction perpendicular to the radial direction. Each of the four thin plate portions 23 is arranged at equal intervals in the circumferential direction. The screw hole 24 is arranged between the thin plate portions 23.

[0019] The bridge portion 22 is a flexible bridge. The bridge portion 22 extends radially from the force receiving portion 21 and connects the force receiving portion 21 to the thin plate portion 23. One end of the bridge portion 22 in the radial direction is fixed to the outer edge of the force receiving portion 21. The other end of the bridge portion 22 in the radial direction is fixed to the center of the thin plate portion 23. Each of the four bridge portions 22 extends in each direction of the cross from the center of the force receiving portion 21 and is arranged at equal intervals in the circumferential direction. That is, each of the four bridge portions 22 is arranged at equal intervals around the force receiving portion 21.

[0020] When the force receiving portion 21 receives a load via the force receiving body 30, the bridge portion 22 and the thin plate portion 23 elastically deform. Due to the elastic deformation of the bridge portion 22 and the thin plate portion 23, the position or posture of the force receiving portion 21 changes. The force receiving portion 21 moves from the position in the initial state by a distance corresponding to the magnitude of the force received by the force receiving portion 21 in the direction of the force received by the force receiving portion 21. Or, the posture of the force receiving portion 21 changes from the posture in the initial state by a rotation angle corresponding to the magnitude of the torque in the direction of the torque received by the force receiving portion 21. The initial state is defined as the state before the force receiving portion 21 receives a load. The position is defined as the position in each axial direction of the X-axis, Y-axis, and Z-axis. The posture is defined as the state of the direction by rotation around each axis of the X-axis, Y-axis, and Z-axis.

[0021] In this way, when the force-receiving part 21 receives a load, the thin plate part 23 and the bridge part 22 are distorted, causing the force-receiving part 21 to displace with respect to the fixing part 25. The displacement of the force-receiving part 21 with respect to the fixing part 25 includes both the case where the force-receiving part 21 moves with respect to the fixing part 25 and the case where the posture of the force-receiving part 21 changes with respect to the fixing part 25. When the application of the load to the force-receiving part 21 stops, the force-receiving part 21 returns to its initial position and posture due to the restoring force of the bridge part 22 and the thin plate part 23. Note that it is not limited to the case where both the thin plate part 23 and the bridge part 22 are distorted when the force-receiving part 21 receives a load. When at least one of the thin plate part 23 and the bridge part 22 is distorted when the force-receiving part 21 receives a load, the force-receiving part 21 displaces with respect to the fixing part 25. When the application of the load to the force-receiving part 21 stops, the force-receiving part 21 returns to its initial position and posture due to the restoring force of at least one of the bridge part 22 and the thin plate part 23, which are the elements that have undergone distortion.

[0022] The detection sensitivity of the force sensor 10 is determined by the flexibility of the thin plate part 23 and the flexibility of the bridge part 22. That is, the detection sensitivity of the force sensor 10 depends on the flexibility of the thin plate part 23 and the flexibility of the bridge part 22. The thinner the thickness of the thin plate part 23 or the shorter the length of the thin plate part 23 in the Z direction, the higher the flexibility of the thin plate part 23. The shorter the length of the bridge part 22 in the Z direction or the shorter the length of the bridge part 22 in the direction perpendicular to the Z axis and the radial direction, the higher the flexibility of the bridge part 22. However, the higher the flexibility of the thin plate part 23 and the bridge part 22, the more the detection sensitivity is improved. On the other hand, the thin plate part 23 and the bridge part 22 are more likely to be damaged, and the fatigue life of the force sensor 10 may not be satisfied. The flexibility of the thin plate part 23 and the bridge part 22 is set so as to satisfy both the detection sensitivity and the fatigue life.

[0023] The magnet mounting plate 40 is made of a steel material. The magnet mounting plate 40 functions as a yoke for amplifying the magnetic flux density of the magnet 60. The force sensor 10 can improve the detection sensitivity by amplifying the magnetic flux density of the magnet 60 with the magnet mounting plate 40 that functions as a yoke.

[0024] As shown in FIG. 5, the magnet mounting plate 40 is fastened to the force receiving portion 21 by a fixing tool 81 such as a screw. The surface of the force receiving portion 21 on the minus Z direction side is in contact with the magnet mounting plate 40. As the force receiving portion 21 is displaced with respect to the fixed portion 25, the magnet mounting plate 40 is also displaced with respect to the fixed portion 25. The displacement of the magnet mounting plate 40 with respect to the fixed portion 25 includes the case where the magnet mounting plate 40 moves with respect to the fixed portion 25 and the case where the posture of the magnet mounting plate 40 changes with respect to the fixed portion 25. When the force receiving portion 21 returns to the initial position and posture, the magnet mounting plate 40 also returns to the initial position and posture.

[0025] FIG. 7 is a view showing a state in which the substrate 50 and the magnetic sensor 70 are removed from the force sensor 10 shown in FIG. 4. In the XY plane shown in FIG. 7, the magnet mounting plate 40 is cross-shaped. That is, each of the four portions of the magnet mounting plate 40 extends in each direction of the cross. The cross formed by the four portions of the magnet mounting plate 40 is the same as the cross formed by the four bridge portions 22. The central portion of the cross of the magnet mounting plate 40 is fastened to the force receiving portion 21. Note that the magnet mounting plate 40 may have any shape as long as it can be fastened to the force receiving portion 21 and can satisfy the function of the yoke, and may have a shape other than the cross shape. The magnet mounting plate 40 may be, for example, a diamond shape or the like.

[0026] The substrate 50 shown in FIG. 4 constitutes the bottom surface of the force sensor 10 on the minus Z direction side. The substrate 50 is fixed to the fixed portion 25 in a state of being in contact with only the fixed portion 25 of the strain generating body 20. The screw holes 51 are formed near the outer edges of the substrate 50 in the X direction and the Y direction. The number of the screw holes 51 is arbitrary. As shown in FIG. 5, the substrate 50 is fastened to the fixed portion 25 by a fixing tool 82 such as a screw screwed into the screw holes 51.

[0027] The force sensor 10 includes four magnets 60a, 60b, 60c, and 60d shown in FIG. 7. Note that the magnet 60 is a term used without distinguishing each of the four magnets 60a, 60b, 60c, and 60d. Each of the four magnets 60a, 60b, 60c, and 60d is attached to the magnet mounting plate 40. Each magnet 60a, 60b, 60c, and 60d is arranged one by one at each of the four portions extending in each direction of the cross on the magnet mounting plate 40. Each magnet 60a, 60b, 60c, and 60d is arranged at a portion of the magnet mounting plate 40 facing the substrate 50. Each magnet 60a, 60b, 60c, and 60d is arranged at a position on the minus Z direction side of the bridge portion 22, that is, at a position on the substrate 50 side with respect to the bridge portion 22. The positions of each magnet 60a, 60b, 60c, and 60d in the XY plane coincide with the positions of each bridge portion 22 in the XY plane. Each magnet 60a, 60b, 60c, and 60d is arranged at equal intervals in the circumferential direction, similar to each of the four bridge portions 22. In addition, each magnet 60a, 60b, 60c, and 60d is arranged at a position at an equal distance from the center of the force receiving portion 21.

[0028] Each magnet 60a, 60b, 60c, and 60d is a permanent magnet or an electromagnet. In Embodiment 1, each magnet 60a, 60b, 60c, and 60d has a hollow cylindrical shape. Each magnet 60a, 60b, 60c, and 60d may have a shape other than the hollow cylindrical shape, such as a solid cylindrical shape or a prismatic shape without a gap.

[0029] FIG. 8 is a plan view showing the substrate 50 and the magnetic sensor 70, which are components of the force sensor 10 according to Embodiment 1. FIG. 8 shows a view of the substrate 50 and the magnetic sensor 70 arranged on the substrate 50 as seen from the plus Z direction side. The force sensor 10 includes four magnetic sensors 70a, 70b, 70c, and 70d. Note that the magnetic sensor 70 is a term used without distinguishing each of the four magnetic sensors 70a, 70b, 70c, and 70d. Each of the four magnetic sensors 70a, 70b, 70c, and 70d is arranged on the substrate 50 and faces the magnets 60a, 60b, 60c, and 60d one-to-one.

[0030] Each of the four magnetic sensors 70a, 70b, 70c, and 70d is an integrated circuit that detects the magnetic flux density in the directions of the X-axis, Y-axis, and Z-axis. Each of the four magnetic sensors 70a, 70b, 70c, and 70d may be a combination of three Hall elements. Each of the three Hall elements detects the magnetic flux density in the direction of one axis.

[0031] The magnetic sensor 70a is arranged facing the magnet 60a. The magnetic sensor 70a is arranged in the magnetic field formed by the magnet 60a. The magnetic sensor 70b is arranged facing the magnet 60b. The magnetic sensor 70b is arranged in the magnetic field formed by the magnet 60b. The magnetic sensor 70c is arranged facing the magnet 60c. The magnetic sensor 70c is arranged in the magnetic field formed by the magnet 60c. The magnetic sensor 70d is arranged facing the magnet 60d. The magnetic sensor 70d is arranged in the magnetic field formed by the magnet 60d.

[0032] As the position of the magnet 60a changes with the displacement of the magnet mounting plate 40, the relative position between the magnet 60a and the magnetic sensor 70a changes. When the relative position between the magnet 60a and the magnetic sensor 70a changes, the magnetic flux density detected by the magnetic sensor 70a changes. The force sensor 10 detects the change in the position of the magnet 60a in each of the three axes based on the change amount of the magnetic flux density in each of the three axes. Thus, the combination of the magnet 60a and the magnetic sensor 70a functions as a three-dimensional position sensor. The combinations of the magnet 60b and the magnetic sensor 70b, the magnet 60c and the magnetic sensor 70c, and the magnet 60d and the magnetic sensor 70d also function as three-dimensional position sensors in the same manner as the combination of the magnet 60a and the magnetic sensor 70a.

[0033] The force sensor 10 uses these four three-dimensional position sensors to detect the change in the position of the magnet 60 at four points on the substrate 50. The force sensor 10 detects the movement of the force receiving part 21 in each of the three axes and the rotation of the force receiving part 21 about each of the three axes by using the position information obtained by these four three-dimensional position sensors.

[0034] By measuring in advance the amount of movement of the force receiving part 21 with respect to the magnitude of the force applied to the force receiving part 21, a conversion rule representing the relationship between the magnitude of the force and the amount of movement is obtained. Based on such a conversion rule, the force sensing sensor 10 obtains the magnitude of the force received by the force receiving part 21 by converting the amount of movement of the force receiving part 21 into the magnitude of the force. Further, by measuring in advance the amount of rotation of the force receiving part 21 with respect to the torque applied to the force receiving part 21, a conversion rule representing the relationship between the torque and the amount of rotation is obtained. Based on such a conversion rule, the force sensing sensor 10 obtains the torque received by the force receiving part 21 by converting the amount of rotation of the force receiving part 21 into the torque. Thereby, the force sensing sensor 10 measures the forces in the three axial directions and the torques about each of the three axes.

[0035] Each of the magnets 60a, 60b, 60c, and 60d is arranged at a position that is at an equal distance from the center of the force receiving part 21 and is arranged at equal intervals. Also, each of the magnetic sensors 70a, 70b, 70c, and 70d faces the magnets 60a, 60b, 60c, and 60d one-to-one. By arranging the magnets 60a, 60b, 60c, and 60d and the magnetic sensors 70a, 70b, 70c, and 70d in this way, the constitutive equation of the above conversion rule can be made into a simpler equation.

[0036] In addition to the components described in the first embodiment, the force sensing sensor 10 includes a cover or the like that covers the force sensing sensor 10 from each of the positive Z direction and the negative Z direction. Also, an electric circuit connected to the magnetic sensor 70 is provided on the substrate 50. Further, the force sensing sensor 10 includes an arithmetic circuit that performs an arithmetic operation based on the above conversion rule, and a display unit that displays the arithmetic result. Since known components can be used for these components, illustration and detailed description of these components are omitted.

[0037] The force sensor 10 according to Embodiment 1 can reduce the number of components and can have a simple configuration as compared with the case where a large number of strain gauges need to be attached to the strain body as in the configuration of Patent Document 1 above. When the strain gauge is directly attached to the strain body, there may be a problem that the adhesive force decreases due to repeated force applied to the strain gauge, and the strain gauge peels off. Since the force sensor 10 does not require attachment of the strain gauge, such a problem can be avoided.

[0038] In the configuration of Patent Document 2 above, since a plurality of leaf springs are used as the strain portion, the response of the Hall element may vary due to manufacturing variations of the leaf springs. Further, in the configuration of Patent Document 2 above, when instead of providing the leaf spring, an elastic body made of a polymer material is used to fill the gap between the Hall element and the permanent magnet, there is a problem that the fatigue life is shortened because force directly acts on the elastic body. The force sensor 10 according to Embodiment 1 can reduce the variation in response due to manufacturing variations because it detects the movement and rotation of the force receiving portion 21 by utilizing the flexibility between the thin plate portion 23 and the bridge portion 22. Further, since the force sensor 10 does not need to be filled with an elastic body made of a polymer material between the magnet 60 and the magnetic sensor 70, the problem of shortening the fatigue life can be avoided.

[0039] Furthermore, the force sensor 10 includes a plurality of magnets 60a, 60b, 60c, 60d attached to the magnet mounting plate 40, and magnetic sensors 70a, 70b, 70c, 70d that detect the magnetic flux density in each of the three mutually perpendicular directions. The force sensor 10 can detect the forces in each of the three mutually perpendicular directions and the torques centered on each of the three axes without increasing the number of components as compared with the case of the configuration of Patent Document 2 above.

[0040] As described above, the force sensor 10 according to Embodiment 1 has the effect that it can have a simple structure and can detect the forces in each of the three mutually perpendicular directions and the torques centered on each of the three axes.

[0041] The configurations shown in the above embodiments are examples of the content of the present disclosure. The configurations of the embodiments can be combined with other known technologies. It is possible to omit or change a part of the configuration of the embodiments without departing from the gist of the present disclosure.

Description of Reference Numerals

[0042] 10 Force sensor, 20 Distortion generating body, 21 Force receiving part, 22 Bridge part, 23 Thin plate part, 24, 31, 32, 51 Screw holes, 25 Fixing part, 30 Force receiving body, 40 Magnet mounting plate, 50 Substrate, 60, 60a, 60b, 60c, 60d Magnets, 70, 70a, 70b, 70c, 70d Magnetic sensors, 81, 82 Fasteners.

Claims

1. It has a fixing part, a force-receiving part that receives a load, a thin plate part provided on the fixing part, and a bridge part that connects the force-receiving part to the thin plate part. When the force-receiving part receives the load, at least one of the thin plate part and the bridge part is distorted, causing the force-receiving part to move or rotate with respect to the fixing part, which is a strain-generating body, A magnet mounting plate fastened to the force-receiving part, A plurality of magnets attached to the magnet mounting plate, A substrate fixed to the fixing part, A plurality of magnetic sensors, each of which is arranged on the substrate, faces the magnet one-to-one, and detects the magnetic flux density in each of the three mutually perpendicular directions, A force sensor characterized by comprising the above.

2. The strain-generating body has a plurality of the bridge parts, Each of the plurality of bridge parts is arranged at equal intervals around the force-receiving part, The magnet mounting plate is sandwiched between the strain-generating body and the substrate, The force sensor according to claim 1, characterized in that each of the plurality of magnets is arranged at a portion of the magnet mounting plate facing the substrate.

3. The force sensor according to claim 1 or 2, characterized in that the magnet mounting plate is made of a steel material.

4. The force sensor according to any one of claims 1 to 3, characterized in that each of the plurality of magnets is arranged at equal intervals and at positions equidistant from the center of the force-receiving part.

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